I take this song as for a person that did everything posible to be liked - loved by the person she loves, but finds a void instead.

She made her seem happy, even though maybe she was sad for a previous relationship, weary ("I took their smiles and I made them mine").
"I sold my soul just to hide the light", the same, she made herself the way she thought the other person wants her to be, even if that made her less of what really she is.

And she sees even though all the effort she's made for that person, all that she changed, she can see how they are both distancing from each other.
She doesn't give up on that love, she runs to and calls out that person, and she knows the other person knows what she feels... she sees that, but still, can't help feeling nothing from the other side, as if the other person does not care.

Even she has tried to be away herself, maybe 'cause she realized that they aren't going anywhere.. like no future in that relationship ("tried to forget you") but you can't forget true love ("but without you I feel nothing") so she asks that person to see her and to love her, because alone without the other person's love, she feels dying ("don't leave me here, by myself I can't breathe").

No matter how, she wants to be with that person, no matter anything, so as above, she runs and calls and begs to be loved back.

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